1. Field of the Invention
The present invention relates to a novel and useful curable resin composition, paint using this curable resin composition, and coat-finishing method which applies this aforementioned paint. In particular, the present invention relates to curable resin composition possessing a high solid content, a novel and useful high solid content-type paint which utilizes this aforementioned curable resin composition of a high solid content, and a novel coat-finishing method for effectively applying this aforementioned high solid content-type paint.
More concretely, according to an aspect of the present invention, a curable resin composition containing at least one specific compound is provided, wherein the specific compound is selected from the group consisting of compounds possessing four functional groups: a blocked hydroxyl group (i) which forms a free hydroxy group by easily cleaving thereof by means of a water in the atmosphere and an application of heat (hereafter referred to as "blocked hydroxyl group"); epoxy group (ii); acid anhydride group (iii); and hydrolytic silyl group (iv), and wherein the blocked hydroxyl group (i) and epoxy group (ii) are incorporated into a vinyl polymer having a number average molecular weight of not greater than 1,500, the acid anhydride group (iii) is incorporated into a vinyl polymer having a number average molecular weight of not greater than 1,500 or an acid anhydride having a number average molecular weight of not greater than 1,500, and the hydrolytic silyl group is incorporated into a vinyl polymer having a number average molecular weight of not greater than 5,000 or a hydrolytic silyl group-containing compound having a number average molecular weight of not greater than 5,000.
In other words, a curable resin composition is provided which contains as essential coating components a compound having a specific molecular weight range and possessing blocked hydroxyl group and at least one functional group selected from the group consisting of acid anhydride group, epoxy group, and hydrolytic silyl group (hereafter referred to as "acryl oligomer"); and a compound possessing a hydrolytic silyl group and at least one functional group selected from the group consisting of blocked hydroxyl group, epoxy group, and acid anhydride group.
In addition, according to second aspect of the present invention, a paint is provided which employs, as an essential binder component, a curable resin composition, as obtained in the aforementioned, principally comprising a so-called low-viscosity acryl oligomer in which hydroxyl group is "blocked" by a specific compound.
According to a third aspect of the present invention, a coat-finishing method is provided which employs a curable resin composition principally comprising a so-called low-viscosity acryl oligomer in which hydroxyl group is "blocked" by a specific compound and a paint for use as a clear coat in a 1-coat .cndot. 1-bake system, 2-coat .cndot. 1-bake system, 2-coat .cndot. 2-bake system, 3-coat .cndot. 2-bake system, and overcoat system.
2. Relevant Art
In recent years, line coating performed by conducting a two-coat-one-bake (2C-1B) finish using a combination of an acryl polyol and a melamine resin is being used in the shell plate coating of vehicles. However, from this coating line, a number of problems have arisen such as speeding of the global warming phenomenon attributed to the release of a large amount of solvents into the atmosphere, as well as combustion processing of these emitted solvents and formation of a large quantity of carbon dioxide.
The prospects for imparting aqueous characteristics to, in particular, the base coat are currently being widely examined. With regard to the clear coat, coating layer qualities such as an attractive external appearance and a high durability are desirable. In addition, water base paints, powder paints, ultra-violet light hardened paints and the like are similarly under extensive examination, however, the closest potential solution appears to lie in the reduction of solvents of conventional resins.
In the case when molecular weight reduction is conducted in order to achieve a high solid content, using a combination formed from acryl polyol-melamine resin according to the conventional art, a large amount of hydroxyl groups must be incorporated in order to compensate for insufficient hardening. However, according to this process, it is not always possible to achieve a low viscosity. Moreover, a coating layer which has been formed by means of hardening a resin with a high hydroxyl group value using a melamine resin leads to an extreme reduction of the acid resistance. In addition, at the time of coating, inconveniences occur such as a remarkable generation of drip-runs along the longitudinal face accompanying a reduction in the viscosity.
In addition, a method is currently being examined for testing solvent reduction by means of using a special portion from the structure of the polymer itself such as a star polymer or the like.
Consequently, it is an objective of the present invention to provide a curable resin composition with a high solid content, and a high solid content-type paint, both possessing an extremely high utility in which a low viscosity is achieved, as well as an improved resistance to acid and abrasion wherein air bubbles and drip-runs are not generated such that the aforementioned various problems with the conventional art are solved. In addition, it is an objective of the present invention to provide a coat-finishing method for coat-finishing a paint with a high solid content and an extremely high utility wherein the aforementioned properties are significantly improved.